Radiation-Induced Polymerization of Urea Canal Complex. Part 4. Radiation-Induced Polymerization of Acrylonitrile in Urea-Ethylene Glycol Supercooled Liquid System

Abstract

Using elementary analysis, NMR on ^{3 1}P and ¹H nuclei, and electroconductivity methods, the acrylonitrile, methacrylonitrile, formaldehyde, and β-propiolactone anionic polymerization in the presence of triethylphosphine is shown to follow the macrozwitterion mechanism: quartary phosphonium being on one end of a polymer chain and the growing anion on the other. The number of covalent bonds through the whole polymer chain between charges forming the active center increases with the propagation reaction. The active centers stationary concentration in the system is low when connected with both the slow initiation reaction and with the fast active centers termination reaction. Thus the ion interaction of different growing polymer chains can be ignored. The active centers parts occurring in the form of ion pairs (the ends are near and form the “cyclic”) and of free ions (the ends are separated) are determined by the monomolecular equilibrium, and its constant depends upon the macro-zwitterion polymerization degree K_d ⁽ⁿ⁾ = K_d ^(I)n^3/2. Such constant depends upon the chain length affords the macrozwitterion self-accelerated propagation with its length, as the free ion reactivity is more than that of ion pairs. The self-accelerated chain propagation effect shows up as an increase of polymerization initial rate order and polymer molecular weight in the monomer concentration. This effect can be avoided by the introduction of electrolyte into the system, which dissociates into ions and transforms all cyclic ion pairs into the linear form, the latter dissociating independently of chain length. The strict mathematical analysis of stationary and nonstationary polymerization kinetics made it possible to determine all the elementary constants separately: K_i = 5.6 × 10^?4 liters/ (mole) (min); K_- = 2.5 × 10⁴ liter/ (mole) (min); K_± = 2.0 liters/ (mole) (min); K_t = 0.84/min; K_t ¹ = 4/min; K_d ^(I) = 10^?4; K₃ = 0.07 × 10^?4 mole/liter.     

Kinetics of Anionic Polymerization of ε-Caprolactone (εCL). Propagation of Poly-ε=CL-K+ Ion Pairs

Kinetics of the anionic polymerization of ε-caprolactone (εCL) initiated with (CH₃)₃SiO^?K⁺ and carried out in THF solution has been studied in the temperature range from 0 to 20°C by using a calorimetric method. From the kinetic results and from conductometric measurements of the dissociation constant of the living Poly-εCL^?K⁺ ion pairs (K_D ²⁰ ? (4 ± 2) × 10^?10 mol/L), we concluded that at the conditions indicated above and for concentrations of active centers ranging from 10^?3 to 3.7 × 10^?2 mol/L, propagation proceeds on the ion pairs and is disturbed neither by dissociation nor by the formation of higher aggregates. For the polymerization of εCL proceeding on the poly-εCL^?K⁺     

Formation of cation–radical anion pairs derived from carboxybenzophenone–tetrabutylammonium salts. Pulse radiolysis studies

Pulse radiolysis of acetonitrile solutions of tetra-n-butyl ammonium salts of 2- and 4-carboxybenzophenones [BP-COO⁻···N⁺(C₄H₉)₄] were performed in order to generate directly the reduced forms of the benzophenone moieties within pre-formed ion pairs. In earlier studies on photochemical electron transfer reactions, ion pairs containing a tetraalkyl ammonium cation and a benzophenone radical anion were formed in an electron transfer to the triplet BP from a quencher consisting of a tetraalkyl ammonium salt of (phenylthio)acetic acid. In the current work, the [BP^•−COO⁻···N⁺(C₄H₉)₄] ion pairs were formed by direct reduction of the salts without the complication of a third moiety, i.e., the (phenylthio)acetic anion. The spectra and kinetic parameters of the radiolytically-reduced salts were compared to the behavior of reduced forms of the 2- and 4-COOH substituted benzophenones. The results from the pulse radiolysis and photochemistry were compared and explained in terms of the different structures of the ion pairs.     

Effects of solvent and counterion on ion pairing and observed charge states of diquaternary ammonium salts in electrospray ionization mass spectrometry

Two diquaternary ammonium chloride salts have been used to examine the roles of solvent and counterion in determination of the degree of ion pairing in solution and the resultant charge state distributions in electrospray ionization mass spectrometry (ESI-MS). Three series of solvents, that is, alcohol, polar aprotic, and chlorinated solvents, have been employed to test the influence of solvent polarity and other parameters on the desorption behavior of diquaternary ammonium ions observed in ESI-MS. Solvents of higher polarity were found to yield gas-phase ions of higher charge states, in accordance with their reduced tendency toward ion pairing in solution. Counterion effects were investigated via the following approaches: (1) increase the diquaternary ammonium salt concentration; (2) increase the concentration of an external electrolyte that contained the common counterion Cl^?; (3) replace Cl^? with trifluoroacetate (TFA_c ^?); (4) increase the concentration of an external electrolyte that contained TFAc^?. These experiments indicate that variation of the specific counterion employed alters the degree of influence that the counterion exerts (via ion pairing) on electrospray ionization mass spectra. Increasing amounts of trifluoroacetate ions in a variety of solvent systems invariably led to a progressive shift of the observed ESI-MS charge states of diquaternary ammonium ions toward lower values.     

Temperature Dependant Micellization of AOT in Aqueous Medium: Effect of the Nature of Counterions

The lithium, potassium, and ammonium salts of bis (2‐ethylhexyl) sulphosuccinic acid have been prepared from the sodium salt (AOT) by applying ion‐exchange technique. The critical micellization concentrations (cmc) of the surfactants with four different counterions have been determined at a temperature range of 10°C to 40°C using surface tension as well as electrical conductivity measurements. Observed data have been utilized to evaluate the ionization degree (counter ion association constant),α, and various thermodynamic parameters of micellization viz, free energy, enthalpy, entropy changes of micelle formation, and also the surface parameters (Γ_max, A_min) in aqueous media. The value of cmc decreases with hydrated ionic size of the counter ions (except K⁺) and follows the order NH₄ ⁺>Na⁺>Li⁺>K⁺. While large negative free energy change (ΔG⁰ _m) and the positive entropy change (ΔS⁰ _m) favor the micellization process thermodynamically, nature of their variation with counterion supports the involvement of counterion size factor in micellization process via a change in the hydrophilicity of surfactant head group.     

Gleichgewichte der Protonenaddition an 1, 1-Bis-(4′, 4″-dimethylaminophenyl)-äthylen in Methanol und in Dimethylsulfoxid

The first and second proton addition equilibrium constants of 1,1-bis-(4′, 4″-dimethylaminophenyl)-ethylene ( 1 ) have been measured by the spectrophotometric method in methanol and in dimethylsulfoxide. Defined as acid dissociation constants of the mono- and diprotonated adduct they are: K₁ (CH₃OH) = 8.3 (± 0.9) · 10^?6M, K₂ (CH₃OH) = 1.22 (± 0.06) · 10^?4M, K₁ (DMSO) = 2.3 (± 0.9) · 10^?3M, K₂ (DMSO) ≥ 1M. The evaluation of the electronic and the NMR. spectra demonstrates that the equilibrium of the two monoprotonated tautomers 2 (methyl-carbenium ion) and 3 (ammonium ion) is, in methanol to about 96% on the side of the ammonium ion (tautomeric equilibrium constant K₂₃ = [3]/[2] ? 23). The tautomer 2 cannot be detected in dimethylsulfoxide. The possible causes of these solvent effects are discussed.     

Electron affinities of higher molybdenum fluorides as determined by the effusion technique

The effusion technique with mass spectral recording of ions was employed to investigate the ionic component of molybdenum trifluoride saturated vapour. The equilibrium constants of ion—molecular reactions involving MoF₅^?, MoF₆^? and MoOF₄^? were measured. The following thermodynamic values were obtained from experimental data: MoF₄(g) + F^?(g) = MoF₅^?(g),ΔH₂₉₈⁰ = ?382.0 ± 20.1 kJ/mole; MoF₅(g) + F^?(g) = MoF₆^?(g), ΔH₂₉₈⁰ = ?413.4 ± 20.1 kJ/mole; MoOF₃(g) + F^?(g) = MoOF₄^?, ΔH₂₉₈⁰ = ?418.0 ± 20.5 kJ/mole; EA(MoF₅ = 3.6 ± 0.2 eV, EA(MoF₆) = 3.6 ± 0.2 eV, EA(MoOF₄) = 4.0 ± 0.4 eV. Reported as well as estimated molecular constants were used to calculate thermodynamic functions of some participants of ion—molecular reactions. For MoOF₃, BeF₃^? and Be₂F₅^? vibration frequencies were calculated from the estimated force field.     

Aggregation and solvation of 9-propylfluorenyllithium and of α,ω-BIS(9-fluorenyllithium)polymethylenes in toluene

Bolaform salts of the type Li⁺,Fl^?(CH₂)_n Fl^?,Li⁺ (Fl^? = 9-fluorenyl, n = 2,4 or 6), when dissolved in toluene, were shown to be present as intramolecular aggregates (λ_m 370 nm) which can be broken up on addition of tetrahydrofuran (THF) or tetrahydropyran (THP) to form solvated tight ion pairs (λ_m 361 nm) and loose ion pairs (λ_m 386 nm). For n = 6 the ratio K₁/K₂ of the loose ion pair formation constants for the two terminal ion pairs is close to the statistical factor 4, but for n = 2 the ratio is only 0.3. This is attributed to a higher stability of the intramolecular aggregate for this compound. The data for the bolaform salts were compared with those obtained for the one ended salt 9-(n-propyl)-fluorenyllithium. For the latter compound, an equilibrium between the monomeric ion pair (λ_m 353 nm) and the dimeric ion pair aggregate (λ_m 370 nm) was found, the dissociation constant K_d being 2.9 X 10^?6M. Addition of THP produces the THP solvated tight ion pair (λ_m 361 nm) and the loose ion pair (λ_m 386 nm).     

Studies of solid-state ion-selective electrodes prepared from semiconducting organic radical-ion salts

The primary redox reactions for solid-state ion-selective electrodes prepared from electronically semiconducting salts of 7,7,8,8-tetracyanoquinodimethane (tcnq) can be identified by considering the redox properties of their constituent ions or molecules. Three different processes involving the couples, Mⁿ⁺/M⁰, 2tcnq^o/(tcnq^-)₂ and (tcnq^-)₂/2tcnq^2- are possible depending on salt composition. Ionic product values determined by potentiometric and atomic absorption methods are in excellent agreement for several such salts; K_s(K₂tcnq₂)=5.8±1.2·10^-11(pot.), 1.7±1·10^-11 (a.a.s.); K_s(Cdtcnq₂) = 3.0±0.5·10^-9 (pot.), 2.9±0.3·10^-9(a.a.s.); K_s(Pbtcnq₂) = 1.3±0.3·10^-10 (pot.), 0.96±0.2·10^-10(a.a.s.); and indicate that the lower activity limit for electrode response is controlled by the solubility of the sensor material itself. Comparisons of predicted and observed standard electrode potentials provide quantitative support for an ion-exchange mechanism of interference. The behaviour of electrodes prepared from Cu₂tcnq₂ (copper(I)) and Cutcnq₂ (copper(II)) is explained on the basis of an interference mechanism and considerations of solid-state equilibria.     

Oxocarbon Salts for Fast Rechargeable Batteries

Oxocarbon salts (M₂(CO)_n) prepared through one‐pot proton exchange reactions with different metal ions (M=Li, Na, K) and frameworks (n=4, 5, 6) have been rationally designed and used as electrodes in rechargeable Li, Na, and K‐ion batteries. The results show that M₂(CO)₅/M₂(CO)₆ salts can insert two or four metal ions reversibly, while M₂(CO)₄ shows less electrochemical activity. Especially, we discover that the K₂C₆O₆ electrode enables ultrafast potassium‐ion insertion/extraction with 212 mA h g^?1 at 0.2 C and 164 mA h g^?1 at 10 C. This behavior can be ascribed to the natural semiconductor property of K₂C₆O₆ with a narrow band gap close to 0.9 eV, the high ionic conductivity of the K‐ion electrolyte, and the facilitated K‐ion diffusion process. Moreover, a first example of a K‐ion battery with a rocking‐chair reaction mechanism of K₂C₆O₆ as cathode and K₄C₆O₆ as anode is introduced, displaying an operation voltage of 1.1 V and an energy density of 35 Wh kg^?1. This work provides an interesting strategy for constructing rapid K‐ion batteries with renewable and abundant potassium materials.     

Caesium as counter-ion in the anionic polymerization of ethylene oxide—II: Kinetics in hmpt

Results are reported for the kinetics of the anionic polymerization of ethylene oxide in hexamethylphosphoramide using the caesium alkoxide of the monoethylether of diethylene glycol as initiator at 40·0°.The reactions were found to be first order in monomer and 0·5 in initiator; rates are depressed by adding caesium tetraphenyl boride. These results indicate that propagation takes place by free ions and ion pairs; the respective propagation rate constants are k_(?) = 22 and k_(±) = 0·2 M 'sec.     

Mass spectrometric characterization of metal triflates and triflimides (Lewis superacid catalysts) by electrospray ionization and tandem mass spectrometry

Trifluoromethylsulfonate (triflate) and bis(trifluoromethylsulfonyl)imide (triflimide) salts, well‐known Lewis acid catalysts, present some difficulty in their characterization. By using nitromethane as the solvent, useful electrospray mass spectra in positive and negative ion mode were obtained for salts of metals in oxidation states +2 and +3. In positive mode, addition of a strong Lewis base (triphenylphosphine oxide, TPPO), capable of displacing a triflate (TfO^?) or a triflimide (Tf₂N^?) anion, is necessary for obtaining useful spectra. Under these conditions of solvent and added ligand, the most abundant ions were [M²⁺(A^?)(TPPO)₂]⁺ or [M³⁺(A^?)₂(TPPO)₂]⁺ with A^? = TfO^? or Tf₂N^?. The MS/MS spectra of these diagnostic ions provide additional analytical information. The breakdown curves, in the form of % dissociated as a function of the ion activation energy, offer a mean for investigating the bonding in these ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Trityl salt—initiated polymerization of α-methylstyrene

The initiation reaction of the polymerization of α-methylstyrene by trityl tetrachloroferate and tritylhexachloroantimonate in 1,2-dichloroethane at 20°C was studied. The rate constants were 14 × 10^?3 and 27 × 10^?3 L mol^?1s^?1, respectively. The dissociation constants of tritylterachloroferate (K_d = 0.88 × 10^?4M^?1) and tritylhexachloroantimonate (K_d = 2.64 × 10^?4M^?1) was determined. The effect of electron acceptors and donors on the dissociation equilibrium and initiation rate was investigated. It was shown that in strongly dissociated ion pairs such as stable carbenium salts the electron donors and acceptors have no appreciable effect on the magnitude of the dissociation. The temperature dependence of the rate constants in the ?20–+20°C range yielded the following thermodynamic parameters for trityltetrachloroferate: E_i = 8.54 kcal/mol; A = 3.2 × 10⁴ mol^?1s^?1; ΔH* = 8 kcal/mol; and S* = ?39.8 eu.     

Electrochemiluminescence Quenching by Halide Ions at Bipolar Electrodes

Quenching of Ru(bpy)₃²⁺ electrochemiluminescence (ECL) by Cl^?, Br^?, and I^? ions was studied as a function of halide concentration in a bipolar electrochemical cell. All of the halides investigated showed similar qualitative behavior: above a critical concentration, ECL intensity was found to decrease linearly as the halide ion concentration was increased, due to dynamic quenching of Ru(bpy)₃²⁺ ECL. Stern‐Volmer slopes (K_SV) of 0.111±0.003, 4.2±0.3, and 6.2±0.3 mM^?1 were measured for Cl^?, Br^? and I^?, respectively. The magnitude of K_SV correlates with halide ion oxidation potential, consistent with an electron transfer quenching mechanism. Using the bipolar platform described herein, aqueous, halide‐containing solutions could be quantified rapidly using the sequential standard addition method. The lower detection limit is determined by a complex mechanism involving the competitive electrooxidation of halide ions and the ECL co‐reactants, as well as the passivation of the surface of the bipolar electrode, and was found to be 0.20±0.01, 0.08±0.01 and 10±1 mM, respectively, for I^?, Br^?, and Cl^?. The performance of the bipolar ECL quenching assay is comparable to previously published fluorescence quenching methods for the determination of halide ions, while being much simpler and less expensive to implement.     

Liquid—liquid distribution of ion associates of tetraiodopalladate(II) with quaternary ammonium counter ions

The distribution behaviour of ion association of Pdl^2?₄ with ten quaternary ammonium cations between chloroform and an aqueous phase was examined and extraction constants (log K_ex) were determined. Linear relationships between log K_ex and the number of methylene groups in the quaternary ammonium ions were observed. Quantitative extraction of palladium was achieved with Zeph⁺ or TBA⁺; the molar absorptivity was 2.5 × 10⁴ l mol^?1 cm^?1 at 344 nm. The effect of other ions on the spectrophotometric determination of palladium, based on their extraction, is reported.     

The cationic polymerization of fluoral—III. Thermodynamics of polymerization in solution

The equilibrium between fluoral in dichloromethane solution and live condensed liquid polyfluoral has been investigated between 22 and 43°C. Equilibrium monomer concentrations gave: ΔH_ac°(298 K) = -50-8 ± 2·3 kJ mol^?1 and ΔS_sc° (298 K) = -142·7 ± 7·4 J K^-1 mol^-1. With the aid of calibration and monomer vaporization data, thermodynamic values for the polymerization of liquid monomer to liquid polymer were also calculated: ΔH_tc° (298 K) = -47 ± 3 kJ mol^-1 and ΔS_1e° (298 K) = -97 ± 10 J K^-1 mol^-1.     

Graft polymerization kinetics of acrylamide initiated by ceric nitrate–dextran redox systems

The kinetics of the graft polymerization of acrylamide initiated by ceric nitrate—dextran polymeric redox systems was studied primarily at 25°C. Following an initial period of relatively fast reaction, the rate of polymerization is first-order with respect to the concentrations of monomer and dextran and independent of the ceric ion concentration. The equilibrium constant for ceric ion—dextran complexation K is 3.0 ± 1.6 l./mole, the specific rate of dissociation of the complex, k_d, is 3.0 ± 1.2 × 10^?4 sec.^?1, and the ratio of polymerization rate constants, k_p/k_t, is 0.44 ± 0.15. The number-average degree of polymerization is directly proportional to the ratio of the initial concentrations of monomer and ceric ion and increases exponentially with increasing extent of conversion. The initial rapid rate of polymerization is accounted for by the high reactivity of ceric ion with cis-glycol groups on the ends of the dextran chains. The polymerization in the slower period that follows is initiated by the breakdown of coordination complexes of ceric ions with secondary alcohols on the dextran chain and terminated by redox reaction with uncomplexed ceric ions.     

Effect of the Counterion on the Cationic Polymerization Rate of Ethylene Oxide by Trityl Salts

The cationic polymerization of ethylene oxide by trityl salts (BF₄ ^?, SbCl₆ ^?, AsF₆ ^?, and PF₆ ^? as counterions) in nitrobenzene at different temperatures has been studied. The kinetic analysis was carried out by use of an automatic manometer, and it showed that the polymerization rate constant depends neither on the counterion type nor on the initial initiator concentration. These facts allowed us to conclude that macrocations and macroion pairs have the same reactivity.     

Metal‐free anionic polymerization of methyl methacrylate in tetrahydrofuran using bis(triphenylphosphoranilydene)ammonium (PNP+) as counterion

Bis(triphenylphosphoranilydene)ammonium (PNP⁺) triphenylmethanide (Ph₃C^–) is a new metal‐free initiator for the living polymerization of methyl methacrylate (MMA). The kinetics of the polymerization strongly depend on the metal counterion of the initiator precursor. When the initiator is made from the metathesis reaction of Ph₃CK and PNPCl, the polymerization follows first‐order kinetics up to 0°C with half‐lives below 0.1 s. The propagation rate constants are much higher than those obtained with tetraphenylphosphonium (TPP⁺) cations, indicating a smaller fraction of dormant ylides. When the initiator is synthesized from Ph₃CLi, polymerization proceeds much slower and molecular weight distributions of the obtained polymers are broadened indicating that the active species are mostly lithium enolates in this case.     

The retro-aldol mechanism in the pyrolysis kinetics of primary,secondary, and tertiary β-hydroxy ketones in the gas phase

The pyrolysis kinetics of primary, secondary, and tertiary β-hydroxy ketones have been studied in static seasoned vessels over the pressure range of 21–152 torr and the temperature range of 190°–260°C. These eliminations are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are expressed by the following equations: for 1-hydroxy-3-butanone, log k₁(s^?1) = (12.18 ± 0.39) ? (150.0 ± 3.9) kJ mol^?1 (2.303RT)^?1; for 4-hydroxy-2-pentanone, log k₁(s^?1) = (11.64 ± 0.28) ? (142.1 ± 2.7) kJ mol^?1 (2.303RT)^?1; and for 4-hydroxy-4-methyl-2-pentanone, log k₁(s^?1) = (11.36 ± 0.52) ? (133.4 ± 4.9) kJ mol^?1 (2.303RT)^?1. The acid nature of the hydroxyl hydrogen is not determinant in rate enhancement, but important in assistance during elimination. However, methyl substitution at the hydroxyl carbon causes a small but significant increase in rates and, thus, appears to be the limiting factor in a retroaldol type of mechanism in these decompositions. © John Wiley & Sons, Inc.